// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// See net/disk_cache/disk_cache.h for the public interface.

#ifndef NET_DISK_CACHE_BLOCKFILE_RANKINGS_H_
#define NET_DISK_CACHE_BLOCKFILE_RANKINGS_H_

#include <list>
#include <memory>

#include "base/macros.h"
#include "net/disk_cache/blockfile/addr.h"
#include "net/disk_cache/blockfile/mapped_file.h"
#include "net/disk_cache/blockfile/storage_block.h"

namespace disk_cache {

class BackendImpl;
struct LruData;
struct RankingsNode;
typedef StorageBlock<RankingsNode> CacheRankingsBlock;

// Type of crashes generated for the unit tests.
enum RankCrashes {
    NO_CRASH = 0,
    INSERT_EMPTY_1,
    INSERT_EMPTY_2,
    INSERT_EMPTY_3,
    INSERT_ONE_1,
    INSERT_ONE_2,
    INSERT_ONE_3,
    INSERT_LOAD_1,
    INSERT_LOAD_2,
    REMOVE_ONE_1,
    REMOVE_ONE_2,
    REMOVE_ONE_3,
    REMOVE_ONE_4,
    REMOVE_HEAD_1,
    REMOVE_HEAD_2,
    REMOVE_HEAD_3,
    REMOVE_HEAD_4,
    REMOVE_TAIL_1,
    REMOVE_TAIL_2,
    REMOVE_TAIL_3,
    REMOVE_LOAD_1,
    REMOVE_LOAD_2,
    REMOVE_LOAD_3,
    MAX_CRASH
};

// This class handles the ranking information for the cache.
class Rankings {
public:
    // Possible lists of entries.
    enum List {
        NO_USE = 0, // List of entries that have not been reused.
        LOW_USE, // List of entries with low reuse.
        HIGH_USE, // List of entries with high reuse.
        RESERVED, // Reserved for future use.
        DELETED, // List of recently deleted or doomed entries.
        LAST_ELEMENT
    };

    // This class provides a specialized version of scoped_ptr, that calls
    // Rankings whenever a CacheRankingsBlock is deleted, to keep track of cache
    // iterators that may go stale.
    class ScopedRankingsBlock : public std::unique_ptr<CacheRankingsBlock> {
    public:
        ScopedRankingsBlock();
        explicit ScopedRankingsBlock(Rankings* rankings);
        ScopedRankingsBlock(Rankings* rankings, CacheRankingsBlock* node);

        ~ScopedRankingsBlock()
        {
            rankings_->FreeRankingsBlock(get());
        }

        void set_rankings(Rankings* rankings)
        {
            rankings_ = rankings;
        }

        // scoped_ptr::reset will delete the object.
        void reset(CacheRankingsBlock* p = NULL)
        {
            if (p != get())
                rankings_->FreeRankingsBlock(get());
            std::unique_ptr<CacheRankingsBlock>::reset(p);
        }

    private:
        Rankings* rankings_;
        DISALLOW_COPY_AND_ASSIGN(ScopedRankingsBlock);
    };

    // If we have multiple lists, we have to iterate through all at the same time.
    // This structure keeps track of where we are on the iteration.
    struct Iterator {
        Iterator();
        void Reset();

        List list; // Which entry was returned to the user.
        CacheRankingsBlock* nodes[3]; // Nodes on the first three lists.
        Rankings* my_rankings;
    };

    Rankings();
    ~Rankings();

    bool Init(BackendImpl* backend, bool count_lists);

    // Restores original state, leaving the object ready for initialization.
    void Reset();

    // Inserts a given entry at the head of the queue.
    void Insert(CacheRankingsBlock* node, bool modified, List list);

    // Removes a given entry from the LRU list. If |strict| is true, this method
    // assumes that |node| is not pointed to by an active iterator. On the other
    // hand, removing that restriction allows the current "head" of an iterator
    // to be removed from the list (basically without control of the code that is
    // performing the iteration), so it should be used with extra care.
    void Remove(CacheRankingsBlock* node, List list, bool strict);

    // Moves a given entry to the head.
    void UpdateRank(CacheRankingsBlock* node, bool modified, List list);

    // Iterates through the list.
    CacheRankingsBlock* GetNext(CacheRankingsBlock* node, List list);
    CacheRankingsBlock* GetPrev(CacheRankingsBlock* node, List list);
    void FreeRankingsBlock(CacheRankingsBlock* node);

    // Controls tracking of nodes used for enumerations.
    void TrackRankingsBlock(CacheRankingsBlock* node, bool start_tracking);

    // Peforms a simple self-check of the lists, and returns the number of items
    // or an error code (negative value).
    int SelfCheck();

    // Returns false if the entry is clearly invalid. from_list is true if the
    // node comes from the LRU list.
    bool SanityCheck(CacheRankingsBlock* node, bool from_list) const;
    bool DataSanityCheck(CacheRankingsBlock* node, bool from_list) const;

    // Sets the |contents| field of |node| to |address|.
    void SetContents(CacheRankingsBlock* node, CacheAddr address);

private:
    typedef std::pair<CacheAddr, CacheRankingsBlock*> IteratorPair;
    typedef std::list<IteratorPair> IteratorList;

    void ReadHeads();
    void ReadTails();
    void WriteHead(List list);
    void WriteTail(List list);

    // Gets the rankings information for a given rankings node. We may end up
    // sharing the actual memory with a loaded entry, but we are not taking a
    // reference to that entry, so |rankings| must be short lived.
    bool GetRanking(CacheRankingsBlock* rankings);

    // Makes |rankings| suitable to live a long life.
    void ConvertToLongLived(CacheRankingsBlock* rankings);

    // Finishes a list modification after a crash.
    void CompleteTransaction();
    void FinishInsert(CacheRankingsBlock* rankings);
    void RevertRemove(CacheRankingsBlock* rankings);

    // Returns false if node is not properly linked. This method may change the
    // provided |list| to reflect the list where this node is actually stored.
    bool CheckLinks(CacheRankingsBlock* node, CacheRankingsBlock* prev,
        CacheRankingsBlock* next, List* list);

    // Checks the links between two consecutive nodes.
    bool CheckSingleLink(CacheRankingsBlock* prev, CacheRankingsBlock* next);

    // Peforms a simple check of the list, and returns the number of items or an
    // error code (negative value).
    int CheckList(List list);

    // Walks a list in the desired direction until the nodes |end1| or |end2| are
    // reached. Returns an error code (0 on success), the number of items verified
    // and the addresses of the last nodes visited.
    int CheckListSection(List list, Addr end1, Addr end2, bool forward,
        Addr* last, Addr* second_last, int* num_items);

    // Returns true if addr is the head or tail of any list. When there is a
    // match |list| will contain the list number for |addr|.
    bool IsHead(CacheAddr addr, List* list) const;
    bool IsTail(CacheAddr addr, List* list) const;

    // Updates the iterators whenever node is being changed.
    void UpdateIterators(CacheRankingsBlock* node);

    // Invalidates the iterators pointing to this node.
    void InvalidateIterators(CacheRankingsBlock* node);

    // Keeps track of the number of entries on a list.
    void IncrementCounter(List list);
    void DecrementCounter(List list);

    bool init_;
    bool count_lists_;
    Addr heads_[LAST_ELEMENT];
    Addr tails_[LAST_ELEMENT];
    BackendImpl* backend_;
    LruData* control_data_; // Data related to the LRU lists.
    IteratorList iterators_;

    DISALLOW_COPY_AND_ASSIGN(Rankings);
};

} // namespace disk_cache

#endif // NET_DISK_CACHE_BLOCKFILE_RANKINGS_H_
